This invention relates to heat exchangers, and more particularly, to an improved tube intended for use in serpentine fin heat exchangers, particularly aluminum heat exchangers or other heat exchangers which are brazed into a final assembly. The invention also relates to a heat exchanger incorporating the improved tube as well as a method of making heat exchangers.
In the manufacture of flat or oval tube/serpentine fin heat exchangers, a common step involves alternating pre-cut lengths of straight, flattened tube with serpentine fins. The result is a multi-layer sandwich that may be flanked on opposite sides by end pieces. This sandwich is made on a planar surface which is intended to provide support for the tubes, the fins and the end pieces to place them in a single plane. The sandwich assembly is located in ajig or a fixture which is intended to hold the heat exchanger components in a planar configuration through a brazing operation wherein all the components are metallurgically bonded together. Because it is not practical to maintain contact of every part of every component with a planar support surface during the brazing operation and still maintain an efficient brazing process, conventionally, the jig or fixture will engage the tubes and serpentine fins only at their ends. Frictional contact between the end pieces, fins and tubes is relied upon to maintain the components in a planar configuration.
Unfortunately, this method of assembly does not always operate as planned. Those skilled in the art will readily recognize that to braze components together, particularly in the case of aluminum or aluminum alloys as the temperature of the components is elevated towards the brazing temperature, all of the components soften substantially. This is particularly true of the serpentine fins which typically have a thickness half or less of the thickness of the tube wall of the tubes. Consequently, as the fins soften, the ability to grasp them frictionally between the tubes may be lost at one or more places along the face of the heat exchanger. When such occurs, the fins sag or droop under their own weight and partially or wholly droop or descend below the desired plane. In mild cases, essentially only the aesthetic appearance of the heat exchanger is affected. That is to say, operational efficiency of the heat exchanger or its ability to be used in an intended environment is not impaired. However, the appearance of being improperly made is a detriment with which manufacturers must be concerned and consequently, such a heat exchanger may be unsaleable.
In other cases, the drooping is so severe that the front to back dimension of the heat exchanger is increased to the point that the heat exchanger cannot be utilized in its intended environment because of the increased depth of its core. In such cases, efficiency may also be impaired because at locations where the drooping occurs, much of the fin crests will be out of contact with the tube and fin side heat exchange will be lowered substantially.
There have been attempts to solve this problem and the same typically focus on placing a recess in the crests of the serpentine fin. The recess is conventionally configured to match the shape of one half of the tube if the tube were separated along its major dimension. As a consequence, at both edges of the fin, tongues which may embrace both the leading and trailing edges of the tube within the heat exchanger are produced. When the sandwich of heat exchanger components is made, these tongues prevent the serpentine fins from descending from their desired positions between the tubes because the tongues partially overlie either the leading or trailing edge of the tubes in the heat exchanger. While such an approach is operative for its intended purpose, properly forming the recesses in the crests of the fins is not a totally uncomplicated process and thus adds to the expense of manufacture. Moreover, if one or more recesses are not formed or are only partially formed, distortion of the fins will result in the final product which may make the same unsaleable simply from an aesthetic standpoint.
The present invention is directed to overcoming one or more of the above problems.
It is one principal object of the invention to provide a heat exchanger that may be economically manufactured and which includes flattened tubes and serpentine fins wherein difficulties associated with fin fall-out or sagging during a brazing process are avoided.
It is also a principal object of the invention to provide a new and improved tube for use in the manufacture of flattened tube/serpentine fin heat exchangers which minimizes or eliminates the possibility of fin fall-out during the manufacturing process.
It is still another principal object of the invention to provide a method of making flattened tube/serpentine fin heat exchangers that minimizes or eliminates the possibility of fin drooping or fall-out during the manufacturing process.
According to the first mentioned object stated above, there is provided a brazed heat exchanger that includes a plurality of runs of a flattened tube having opposite flattened side walls, spaced opposite end walls interconnecting the side walls and at least one interior row of ports. The distance between the end walls is substantially greater than the distance between the side walls and such distances respectively define a tube major dimension and a tube minor dimension. A ridge is located on and projects outwardly from each side wall away from the row of ports a relatively short distance and serpentine fins are located between each of the runs and have crests brazed to the side walls of the runs adjacent thereto. The crests are slightly deformed by the ridges whereby the ridges lock the fins between the runs during a brazing process.
In a preferred embodiment, the tube runs, ridges and fins are formed of aluminum.
Preferably, the tube or tubes of which the runs are formed are extruded.
According to another facet of the invention, a tube for use in a heat exchanger of the type having serpentine fins located between parallel tubes disposed in a row is provided. The tube is a flattened tube or oval having opposed, flattened, spaced side walls interconnected by opposite end walls with the distance between the side walls being less than the distance between the end walls to respectively define a tube minor dimension and a tube major dimension. At least one row of ports extending between the end walls and located within the side walls is provided. Also provided is an elongated ridge on the exterior of each of the side walls that extends outwardly therefrom and away from the row of ports. The ridge is adapted to engage and slightly deform the crests of an adjacent serpentine fin and has a height insufficient to separate the crests from the exterior of the associated side walls sufficiently to prevent the formation of a brazed joint between the fin and the side wall along substantially the entire length of the crest.
Again, in a preferred embodiment, the tube is an extruded aluminum tube.
In one embodiment, each ridge is prism-shaped.
In a preferred embodiment, each of the ridges includes two sides meeting at an apex and in a highly preferred embodiment, the ridge extends away from the associated side wall a distance in the range of about 0.005 inches to about 0.05 inches as measured to the apex.
A preferred embodiment also contemplates that the included angle at the apex is on the order of 90xc2x0.
In one embodiment, the ridges are substantially centered between the end walls of the tube.
According to the third principal object of the invention mentioned above, there is provided a method of brazing a heat exchanger that includes the steps of: a) providing a tube matrix including a plurality of spaced tube runs in a predetermined relation with the runs having flattened sides facing adjacent runs and ridges extending the length of the runs and extending outwardly from the flattened sides thereof, b) locating serpentine fins between adjacent runs with crests of the fins substantially engaging the ridges; c) reducing the spacing between the runs so that c-1) the ridges are driven into the crests to frictionally lock the runs and the fins together and c-2) the crests are brought into substantial abutment with the flattened sides. The method also includes the step of d) subjecting the assembly resulting from step c-1) and c-2) to brazing temperatures for a sufficient period of time to braze the runs and the fins together.
In a preferred embodiment, step a) includes the step of providing an extruded aluminum tube.
According to a preferred embodiment, step a) also includes the step of providing the tube matrix as a plurality of straight tube runs.
In an even more preferred embodiment of the invention, step a) includes the step of providing the straight tube runs as individual pieces of tubes.
A preferred embodiment of the invention contemplates that the ridges be shaped as prisms having a fin engaging apex.
In a highly preferred embodiment of the invention contemplates that the apex extend from the flattened sides at a distance in the range of about 0.005 inches to about 0.05 inches.
In a very highly preferred embodiment, the apexes having an included angle on the order of 90xc2x0.
Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawings.